A mentally ill taxi driver who cut the throat of a stranger at a London tube station has been given a life sentence with a minimum term of eight and a half years after a judge concluded the attacker was motivated by Islamic extremism.

Muhiddin Mire, 30, who has paranoid schizophrenia, told police the rampage in December 2015 was an act of revenge for coalition airstrikes in Syria, which the UK government had voted to support three days previously.

Judge Nicholas Hilliard, the recorder of London, told Mire he would be immediately transferred to Broadmoor, the high-security psychiatric hospital in Berkshire.

The type of sentence handed down to Mire means that if he is found to be free of symptoms and subject to review he could be transferred to prison to serve the remainder of the term.

Hilliard said: “This was an attempt to kill an innocent member of the public for ideological reasons by cutting his throat in plain sight for maximum impact.”

Mire, who had downloaded Islamic State propaganda before the attack, was convicted in June of attempted murder for stabbing 56-year-old Lyle Zimmerman and threatening four other travellers at Leytonstone station, east London.

But doctors giving evidence to the hearing conflicted over whether Mire’s mental illness was the sole reason for the attack.

Dr Shaun Bhattacharjee, a Broadmoor forensic psychiatrist, told the court Mire’s interest in extremism was a symptom of his mental disorder. But Dr Philip Joseph told the judge it was possible for Mire’s obsession with Islamic terrorism to be separate from the illness.

Ultimately, Hilliard sided with Joseph’s argument. “What the defendant was intent upon was designed to intimidate a section of the public that were there to witness what he was doing. This was not carried out in secret but very brazenly indeed. It was carried out to advance a religious or ideological cause, namely Islamic extremism.”

Hilliard said Mire’s interaction with commuters in the tube station during the attack was evidence of his awareness of what was going on around him.

It was revealed during an earlier hearing that Mire was sectioned in 2006 and released with a prescription for antipsychotic medication after two weeks in hospital.

He was put in touch with a community mental health team upon his release but soon lost contact with them and stopped taking the medication. In the years before the attack, Mire became increasingly unwell and was probably already exhibiting symptoms of paranoid schizophrenia.

Among “strange” ideas Mire had was a belief that the former prime minister Tony Blair was his guardian angel and that he had been possessed by evil spirits, the court heard.

His paranoid delusions later manifested in a belief that he was under surveillance by the security services and was being followed.

Bhattacharjee told the court the prevailing culture – in this case a heightened state of tension over Islamic terrorism – could often inform schizophrenics’ delusions. As an example, Bhattacharjee said in the 1970s some paranoid schizophrenics experienced delusions related to the IRA and Irish terrorism.

During the attack, Mire shouted, “This is for my Syrian brothers. I’m going to spill your blood.” But Joseph told the same hearing that this interest in extremism was separate from his mental illness, not fuelled by it.

Mire told police in the hours after his arrest that the attack was an act of vengeance for coalition airstrikes in Syria. On 2 December, the government voted in favour of extending bombings against Isis targets in the Middle East to include Syria.

He had images of the soldier Lee Rigby and a British Isis killer on his phone, along with material linked to the terror group.

The court heard Mire started viewing Isis videos online three years before the attack.

After sentencing, Met police commander Dean Haydon, of the counter-terrorism command, said: “London is a safer place with Mire behind bars. While Mire was not accused of terrorist offences, it would appear from comments he made at the time of the attack and the content he had downloaded on his phone that he may have been inspired by terrorist propaganda.

“My officers continue to work tirelessly in stopping people getting drawn into terrorism and violent extremism in all forms as well as prosecuting, disrupting and deterring extremists, reaching out to communities and safeguarding the vulnerable.

“We depend on information from the public, who can be our eyes and ears in our efforts to keep us all safe.”